Hydrofluorocarbons (HFCs), such as HFC-125 and HFC-32, have been widely used as important substitutes for CFCs, HCFCs, etc., which are known as substances that deplete the ozone layer. Known examples of such substitutes include “HFC-410A,” which is a mixture of HFC-32 and HFC-125, “HFC-404A,” which is a mixture of HFC-125, HFC-134a, and HFC-143a, etc.
Such substitutes have various applications, such as heat transfer media, refrigerants, foaming agents, solvents, cleaning agents, propellants, and fire extinguishers, and are consumed in large amounts. However, since these substances have a global warning potential (GWP) several thousand times higher than that of CO2, many people are concerned that their diffusion may affect global warming. As a global warming countermeasure, the substances are collected after being used; however, not all of them can be collected, and their diffusion due to leakage, etc., cannot be disregarded. For use in refrigerants, heat transfer media, etc., although substitution with CO2 or hydrocarbon-based substances has been studied, CO2 refrigerants have many difficulties in reducing comprehensive greenhouse gas emissions, including energy consumption, because of the requirement of large equipment due to the low efficiency of the CO2 refrigerants. Hydrocarbon-based substances also pose safety problems due to their high flammability.
Hydrofluoroolefins with a low warming potential are recently attracting attention as substances that can solve these problems. Hydrofluoroolefin is a generic name for unsaturated hydrocarbons containing hydrogen, fluorine, and chlorine, and includes substances represented by the following chemical formulae. The description in parentheses following each chemical formula indicates the refrigerant number typically used for refrigerant purposes.
CF3CF═CF2 (HFO-1216yc or hexafluoropropene),
CF3CF═CHF (HFO-1225ye),
CF3CF═CH2 (HFO-1234yf),
CF3CH═CHF (HFO-1234ze),
CF3CH═CH2 (HFO-1243zf)
CF3CCl═CH2 (HCFO-1233xf),
CF2ClCCl═CH2 (HCFO-1232xf),
CF3CH═CHCl (HCFO-1233zd),
CF3CCl═CHCl (HCFO-1223xd),
CClF2CCl═CHCl (HCFO-1222xd),
CFCl2CCl═CH2 (HCFO-1231xf), and
CH2ClCCl═CCl2 (HCO-1230xa).
Of these, fluoropropenes are particularly promising substances as candidates for refrigerants or heat transfer media with a low GWP; however, they may sometimes gradually decompose over time, etc., and thus are not highly stable. Accordingly, these substances have a problem of gradually reducing performance depending on the situation or environment when used in various applications.
To enhance the stability of fluoropropenes, a method for adding a phenol compound to a composition containing HFO-1234yf and CF3I is known (see, for example, Patent Literature 1).